How to create a larger light radius with an HDRI
Judging from the middle grey-ish values on the left and right, something seems incorrect here.

That is, I suspect the albedo values on your floor are too high. We should expect that the direct sun source, which is relatively small, would project sharp and direct heavy light through all three windows. Instead, we barely have middle grey, yet on the centre window, the high energy pixel region is the cumulative effect of fresnel and albedo reflecting the light directly, as opposed to illumination. Hence, wrong values, and too low of an HDRI strength.

I also see skew to yellow there, which suggests Filmic isn't set as the view, or you have a degree of processing that is breaking things. The false colour LUT shouldn't be used with anything other than Filmic.